#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#define _CRT_SECURE_NO_WARNINGS 1
int main()
{
	int a = 0;
	int b = 0;
	int c = 0;
	float s = 0;
	float h = 0;
	scanf("%d%d%d", &a, &b, &c);
	if (a + b > c && a - b < c)
	{
		h = (float)(a + b + c) / 2;
		s = sqrt(h * (h - a) * (h - c) * (h - b));
		printf("%f\n", s);
	}
	else
		return 0;
}
int main()
{
	char ch = 0;
	ch = getchar();
	if (ch >= 65 && ch <= 90)
		printf("%c", ch + 32);
	else
		printf("%c", ch - 32);
	return 0;
}
int main()
{
	int sum = 0;
	int max = 0;
	int min = 0;
	int score = 0;
	int i = 0;
	for (i = 0; i < 4; i++)
	{
		scanf("%d", &score);
		sum += score;
		if (i == 0)
		{
			max = score;
			min = score;
		}
		if (i > 0)
		{
			max = max > score ? max : score;
			min = min < score ? min : score;
		}
	}
	int avg = sum / 4;
	printf("sum = %d\n", sum);
	printf("avg = %d\n", avg);
	printf("max = %d\n", max);
	printf("min = %d\n", min);

}